MRI is one of the major non-invasive imaging modalities in modern clinical diagnosis. Nevertheless, improving image contrast is still a critical, urgent issue in the development of MRI. By utilizing an external electronic device, we can significantly enhance and actively manipulate the feedback field that is suitable for clinical applications. In this study, a new designed electronic feedback device is presented. It is shown that the ability to control the frequency and bandwidth of the feedback field via the feedback loop empowers the feedback-enhanced MRI with applicability and robustness for contrast enhancements in phantom and in vivo tumor images. In phantom experiments, the contrast of magnetizations with same frequency but different frequency distribution can be manipulated by changing the bandwidth of feedback RF field. In tumor detection, the feedback field enhanced images showed higher spatial resolutions and discriminate the regimes of necrosis and activation, which is consistent with the pathologic results.